Heretofore condensates of phenol and formaldehyde have been produced in such a way that phenol dissolved in water was mixed with formaldehyde and sulphuric acid and this reaction mixture heated. After a certain time more formaldehyde solution was added to the reaction mixture increasing the temperature of the whole batch. After the sulphuric acid was neutralized by means of caustic soda, the water added to the batch, as well as that which had been formed during the chemical reaction, was distilled off under vacuum. This procedure entails difficulties in handling, particularly if applied on an industrial scale. The first phase of the reaction is very turbulent due to the formation of exothermic heat. Further non-homogeneities result when the second portion of formaldehyde is added and later on when the caustic soda is added for the neutralization, for the batch at this time has already separated into layers.
Finally the molten product is washed by adding a quantity of water several times greater than that of the product. Difficulties result from carrying out the washing because the melting point of the condensates is over 100.degree. C. The difficulties mentioned have an influence on the properties of the condensates produced, so that products made from these condensates will be non-homogeneous in their properties. It is further known that in producing condensates of phenol and formaldehyde according to the process described there are upper limits for the degree of polymerization which may be attained. The polymerization limits are due to the nature of the reaction between phenol and formaldehyde. There are two possibilities: first, the formation of linear products with a methylene bridge between the phenolic rings and second, the formation of bridges between linear molecular chains (cross-linking). The second-mentioned reaction leads to insoluble and infusible products which cannot be converted into films or threads. If the mol ratio of phenol to formaldehyde is greater than 1, the first mentioned reaction results. Theoretically a relatively high degree of polycondensation may be attained, if the ratio of phenol to formaldehyde is 1.01. In a particular application with a ratio of phenol to formaldehyde of 1.25 the resulting degree of polymerization was 6 to 7. Polymerization of this order of magnitude is considered not suitable for the production of threads.